The heart is generally comprised of four chambers: the left and right atrium, and the left and right ventricle. Additionally, a small cavity called the left atrial appendage (LAA) is located off the left atrium between the mitral valve and the left pulmonary vein. Thus, the LAA opens into the left atrium of the heart. The LAA is shaped like a small thumb which terminates as it tapers away from the opening. The opening itself is referred to as the LAA ostium.
In a healthy heart, the LAA contracts as the heart contracts. In individuals diagnosed with atrial fibrillation (AF), however, the LAA may not contract with enough force to expel all of the blood from the LAA. In individuals diagnosed with AF, the electrical activity of the atrium becomes very rapid and disorganized. Thus, the heart beats quickly and may not get enough time in between beats to fill up with blood. As a result, only a small amount of blood is pumped out of the heart with each beat, and the cardiac output drops significantly. Therefore, stagnant blood may easily remain in the LAA. Because clotting occurs when blood is stagnant, clots or thrombi may form in the LAA. If a blood clot leaves the LAA and becomes lodged in an artery in the brain, a stroke results.
The LAA may be sealed off during open heart surgery, which is a risky, painful, and expensive procedure. Surgery for closure of the LAA is major heart surgery, which requires the patient to undergo general anesthesia and opening of the chest cavity. The patient must spend several days in the hospital and thereafter may take several weeks to be able to return to normal levels of activity.
To avoid the risks and discomfort associated with open heart surgery, modem occlusion devices have been developed that are small, implantable devices capable of being delivered to the heart through a catheter. Rather than surgery, a catheter inserted into a major blood vessel allows an occlusion device to be deployed at the defect once the device has been moved through the catheter to the treatment site. This procedure is performed in a cardiac cathlab and avoids the risks and pain associated with open heart surgery. These devices have proven effective at sealing defects in the heart and could likewise be used to occlude the LAA without requiring open heart surgery.
Devices that have received significant clinical study include the “Plaato” device described in U.S. Pat. No. 6,152,144 among others, and the “Watchman” device described in U.S. Pat. No. 6,689,150 among others. Each of these clinically tested devices lies wholly within the LAA and includes a membrane that spans the opening or ostium of the LAA. The Watchman device is typically porous and in the Plaato device the membrane is impervious to the passage of blood. Additionally, the Watchman device uses a series of barbs or prongs which enter the tissue surrounding the ostium of the left atrial appendage to help secure the device during the acute phase of implant.
While devices such as these have been shown to be effective for occluding the LAA, they nevertheless have drawbacks. For example, such devices are often incapable of being readily deployed in anatomies having irregularities such as an oddly shaped LAA or that extends at sharp angles from the atrial wall. Similarly, such devices employ occluding baskets or cages of wire mesh that though flexible, may impose their shape on the LAA causing the LAA to be distended or irritated leading to potential post implantation complications. The ability to retrieve and redeploy the devices which may be necessary to achieve proper placement is also problematic with these existing devices. In most instances a retrieved device may not be reused and must be replaced, driving the cost of the therapy up.
Thus, there is a need in the art for an LAA occlusion device which can be implanted at a wide variety of approach angles and that may be implanted into the LAA without distorting the shape of the LAA or causing undue irritation thereto; and which is redeployable to facilitate reliable implantation.